D-7 PI Project

		Quote:			Posted by ram
	hello eugene 52 (my idol) i have deepers8 schematic with lay file from g zhelev w/c he corrected. please check this if it's really works. ram,

Hello Ram , Great to see you again !!
I do remember this power supply [fuzzy hand drawing] for the deepers 8 schematic you posted .
I am looking at this now and wondering does this have a 2nd battery to pin3 of IC10a [mc 1458] ?
Power supply has only regulated  -12 and +6 volts output !! Thank-You

Best Regards..... ......Eugene


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Dooley, I suggest that you set up a block diagram of each function you want and how you want to treat it when an object is detected. Design your blocks with as much flexibility as you want to make it function like you want.

My biggest and best project right now has an 8 bit MCU for all signal generation and timing with a 32 bit MCU for all processing. A few low noise op amps scattered around and a multi-node coil are in the mix. I will add a dsPIC later for a 3D target image display later but there is room for it quite easily. The multi-node coil and its controller is a new technology developed by myself that will allow a 3D image of a target in the ground.

Don't get your hopes up on this being the final development of this project. It has the carcasses of 5 previous iterations in the shop just waiting for burial. Actually, they serve to allow me to experiment with an idea now and again. This project is probably 3 years or more away from being complete. Hopefully it will give you some food for thought.

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Yikes! So many questions. Good for you. I'll answer one by one as well as I can. Remember though that some of the readers here are not technically oriented so my explanations may seem a bit too simple for your liking. Bear with it. I just want to be sure that the rank beginner won't lose interest or become lost.

		Quote:			Posted by DOOLEY1972
	HELLO GOLDDIGGER , can i ask a few basic questions that i want to get my head around ?? a while back i was asking about single coil PI's and TX / RX PI's and all though the dual coil rx / tx would be simpler to build i recall you said that i would loose depth / power due to coil interaction / damping , would i loose allot ??

Any metal in proximity to the coil will diminish the coil's efficiency. Plastic screws are often used on plastic lower shafts for that reason. If your coil is not adding to the signal by also being energized, it is a load on your field that is generated. You will not be any better off with two coils in a PI machine.

		Quote:			Posted by DOOLEY1972
	other thing is , if say i had a single coil PI around th 300uH to 400uH region , and was sampling in the 20 - 30 us area , and i then i built coil with a sepperate rx winding ontop of original tx with same number of turns , would this affect / slow down the coil or would i theoreticaly be able to sample at the same time ??

Your field in a PI is always too powerful to allow simultaneous reception. As I said above, if the coil is just resting there, it is a load. If it is active as a receiver, it is still a load because it will absorb some of your field. Forget the dual coil. There are dual coil machines out there but I don't know of any in production today. They are old systems that were proven less efficient than single coil machines.

The TX in a PI machine generates a signal of as much as 800 volts and 35ma to generate a maximum field for any given coil. After generating this enormous pulse and building a massive field, the TX is shut down, the field goes to zero and the same coil is used to sense any field left behind using a very high gain amplifier system. Normally this consists of a series of operational amplifiers with a dual diode input clamping circuit to keep the huge field from sending back a devastatingly large return to the receiver. As you might imagine, having the TX on at the same time as the RX without those clamping diodes would be fatal to the system.

The signal returns are then compared to the original pulse train to see a difference in the return signal. The critical area is the small time between the TX being shut down and the field going to completely zero in strength. That window of time is very small and there is not much difference between the signal for gold and that of iron. Thus, the difficulty of discriminating.

		Quote:			Posted by DOOLEY1972
	next question is a big one that makes no sense to me : we limit the voltage to the first op-amp using back to back diode to limit voltage to op-amp to between 0.5v and 0.7v yes ? but the 1st amp on most designs is set for gain of 1000 using a 1k and a 1M resistor , if we amp 0.7v by 100 we end up with theoretical 700v and in reality the op amp will "rail out" until right near the end. now this is puzzling me , either we amp the 0.7v by gain of 17 to keep it in the 12v window , or the "real signal" we are looking for is realy small , so if the gain is 1000 and our window is say 10v then what we are realy looking at is 10mv is this where all the action takes place ?? and that we are not realy looking at the 0.7v signal , the diodes are only there to protect op amp , so why are there so many pictures of PI decay curves on the net showing 0.7v down to 0v ??

Good question and the answer is very simple. We limit the input so we don't destroy the first stage of amplification. That amplifier is set up in the current mode, not the voltage mode so the amplification is taking the microamps of returned and sensed current and turning them into milliamps so we can generate a usable signal from that very tiny return pulse.

		Quote:			Posted by DOOLEY1972
	so there are my 2 questions that are doing my head in , whats the real voltage of the curve that we want to look at ?? and will dual coils work ??

I would personally never use a dual coil for a PI machine with one exception. A Double D coil with a single winding seems to me a good idea. I think it aids in pinpointing and in signal rejection for nearby large targets. The theory behind that can be demonstrated by building a simple field visualizing circuit. I described one on this forum using a PC sound card and a coil. Search for it.

		Quote:			Posted by DOOLEY1972
	last thing is , why don't PI designers do a simple voltage shift on the first op-amp as well as gain , then that way right after the first op-amp we can be working in the normal 12v window instead of in the range of +7v to +17v ?? only a thought.

There are single voltage operational amplifiers but they are far less efficient that the dual voltage type. The reason is that they use internal charge pumps to generate the negative voltages and thereby fool the internal circuitry into believing there are dual voltages present. Also, a single voltage operational amplifier cannot be used in the current mode so the first stage would be very inefficient.

		Quote:			Posted by DOOLEY1972
	thanks for listening.

Hey, it's fun.

Something you didn't ask about. The single coil generates a pulse and then goes quiet waiting for the receiver to do its thing. Then, after a measured period of time, it sends out another pulse. The time between pulses is a problem for detector users because during your coil swinging, you must develop good habits of slow scanning. If you scan too fast, your receiver is effectively blinded by the fact that you move it away from any fields that may be residual in targets. Some people can swing their coil so fast as to eliminate every target in the area. Slow, steady movement is absolutely essential. At the very outside, I recommend no more than a left right swing of about 1/2 second followed by a right left swing of the same time. A total of 1 second is good.

I have gone behind a fast coil swinger and found things he missed. When I showed him what he was doing and the result, he was very angry at himself for not learning more about his hobby. With a coin buried at 30cm, his technique missed it. When he slowed down, it was a big a signal as you could get. He's a lot happier now.

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http://www.thunting.com/smf/index.php/topic,6550.msg187717.html#msg187717

Hi  all!  "DEEPERS 8" P.SUPPLY :

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Hi GD
is this anything like the double D with a single winding that you have tried or considered ?

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